1. Field of the Invention
This invention relates to internal combustion engines and, more specifically, to internal combustion engines which employ flexible link transmissions, or belts, such as trapezoidal belts, flat belts or multi-rib belts.
2. Description of the Prior Art
The tensioning devices of the prior art exert an elastic force on belts through an idle roller, which is supported at the end of an oscillating arm to which an elastic torque from a spring is applied. Frequently, the roller rolls on the smooth, back side of the belt. Under such circumstances, there is no need for mechanical adherence, or friction, between the roller and the belt. The lever arm pivots on a shaft which supports the elastic tensioning device, thereby forming an assembly hereinafter designated as the "tensioning roller."
Several examples of this type of device are disclosed by German Patent No. 35 28 442, which is assigned to Daimler-Benz; French Patent No. 2.509.408, which is assigned to Litens Automotive; and U.S. Pat. No. 4,472,162, which is assigned to Dyneer Corporation. In the devices disclosed in the latter two patents, a tensioning torque is applied to belts by means of a torsion coil spring and damping is provided by friction applied by rubber rings. In the first cited patent an elastic torque is exerted by means of a of a brake which is controlled by detectors. Such arrangements offer a great deal of flexibility, which makes it possible to provide a constant tension for the flexible link, but the damping of the tension variations subjects the device to random wear by the abrasion or creep of the elastomer compound used for the friction damping. An electromagnetic damping device, of course, can usually only be used in conjunction with expensive sensors and corresponding software.
European Patent No. 114,779, also, relates to a device of the type described above. This patent discloses a device in which an elastic ring is used as a pivot bearing and a torsion spring. The device provides regulation capabilities obtained by rotation of a fixed ring on a socket having a pawl and ratchet mechanism, thereby taking advantage of the axial flexibility of the elastic ring.
The greatest disadvantage of the devices of the prior art relates to the physical dimensions of the tensioning devices necessary to ensure a sufficient degree of tension.